Biomechanical Model Of The Human Female Neck And Head System

Computational models have many advantages in biomechanical analysis. Specifically, we are interested in the role of neck muscles in whiplash injury. Studies have shown that women are more likely to experience whiplash injury than men. A female neck musculoskeletal model is essential for analyzing the gender difference in whiplash, especially the influence of size, geometry and biomechanical properties. A male neck musculoskeletal model [1] has been developed in our lab, but currently a female neck model does not exist. The goal of this study is to develop a biomechanical model of the female head and neck system in SIMM (Software for Interactive Musculoskeletal Modeling; Motion Analysis, Santa Rosa, CA) based upon female anatomy from the National Library of Medicine’s Visible Human Project (VHP).

METHODS

The biomechanical neck model of the musculoskeletal system in SIMM consists of the following components: skeletal anatomy, joint kinematics, muscle anatomy and force-generating parameters.

Skeletal anatomy

Computed Tomographic (CT) images of the Visible Human Female (59 yrs old, 1.65 m tall) were obtained from the National Library of Medicine website. Image analysis software (3D-doctor, Able Software, Lexington, MA) was used to segment bone geometry and visualize the 3D models of the skull and each cervical vertebra. (Fig. 1, Fig. 2)

The vertebrae from the Visible Human Female were scanned in the supine posture (lying on the back), which is most likely different from the upright neutral posture. Thus the relative orientations of vertebrae needed to be adjusted to correspond to the upright neutral posture.

Relative angles between vertebrae were obtained from Harrison, et. al [2], and normalized relative displacement between two vertebrae were obtained from Frobin, et. al [3] to adjust the head and vertebrae to their upright neutral posture in the sagittal plane (Fig. 4). The data used for the model in upright neutral posture are all measured from female subjects.

From the vertebral data we have [2][3], we can know the intervertebral angle α and the relationship among x, y, l, displ and disc height (Hdisc, Δhup and Δhlow ). Solved these equations for x, y and l, which define the upright neutral posture.

Other kinematic data needed are: instantaneous axes of rotation between vertebrae, total range of motion and relative intervertebral motion. Unfortunately, data from female subjects only are not available for all parameters; in some cases mixed male and female data were used.

Muscle anatomy and Force-generating parameters

The origin and insertion of each neck muscle were defined according to the same anatomical landmarks as in the male model, and straight lines were used to represent muscle paths initially. Currently, muscle force-generating parameters (fiber lengths and cross sectional areas) are not available for females.

RESULTS AND DISCUSSION

We have developed the biomechanical model of female head and neck system initially (Fig. 5). Future model development involves using Magnetic Resonance Imaging (MRI) to obtain female neck muscle geometry (volume and path), which allows calculation of muscle force- and moment-generating properties; incorporating curved muscle paths using MRI data; and performing dynamic analyses to address gender differences in neck injury.